This invention relates generally to gas generation such as involved in the inflation of automotive inflatable restraint airbag cushions and, more particularly, to gas generant materials which contain metal complexes of guanylurea nitrate.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an xe2x80x9cairbag cushion,xe2x80x9d that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Such systems typically also include one or more crash sensors mounted on or to the frame or body of the vehicle to detect sudden decelerations of the vehicle and to electronically trigger activation of the system. Upon system actuation, the cushion begins to be inflated in a matter of no more than a few milliseconds with gas produced or supplied by a device commonly referred to as an xe2x80x9cinflator.xe2x80x9d
Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials.
In view thereof, significant efforts have been directed to minimizing or avoiding the use of sodium azide in automotive airbag inflators. Through such efforts, various combinations of non-azide fuels and oxidizers have been proposed for use in gas generant compositions. These non-azide fuels are generally desirably less toxic to make and use, as compared to sodium azide, and may therefore be easier to dispose of and thus, at least in part, found more acceptable by the general public. Further, non-azide fuels composed of carbon, hydrogen, nitrogen and oxygen atoms typically yield all gaseous products upon combustion. As will be appreciated by those skilled in the art, fuels with high nitrogen and hydrogen contents and a low carbon content are generally attractive for use in such inflatable restraint applications due to their relatively high gas outputs (such as measured in terms of moles of gas produced per 100 grams of gas generant material).
In addition to low toxicity and high gas outputs, fuel components for use in gas generant materials desirably are relatively inexpensive, thermally stable (i.e., desirably decompose only at temperatures greater than about 160xc2x0 C.), and have a low affinity for moisture.
Oxidizers known in the art and commonly employed in such gas generant compositions are metal oxides or salts of oxygen-bearing anions (e.g., nitrates, perchlorates, etc.). During combustion, the metallic component of such oxidizers, however, typically ends up as a solid. Thus, the amount of oxidizer included in such gas generant materials can significantly effect the amount of gas produced upon combustion of the gas generant material. In view thereof, efforts have been directed to reducing or minimizing the amount of oxidizer required in such gas generant formulations. One approach used with at least some success in reducing or minimizing the required amount of oxidizer involves the incorporation of oxygen in greater relative amounts in the fuel component of the gas generant composition. Thus, desirable fuels for use in such gas generant compositions may preferably include a relatively high content of oxygen.
An additional complication results from the fact that at least certain transition metal-containing compounds or materials, such as commonly employed transition metal-containing oxidizers, may undesirably react with other composition materials to form metallic derivatives of a highly explosive nature and such as are unsuited for various general uses such as in an automotive inflatable restraint system or a gas generating device used in such a safety system. Thus, when including transition metal-containing compounds or materials in such formulations care is required to ensure that the formulation does not also include a material which may undesirably react therewith to form such explosive metallic derivatives.
U.S. Pat. No. 6,024,812 discloses propellant formulations which include nitroaminoguanidine as a main component, a secondary fuel or explosive ingredient such as dicyandiamidine nitrate (also known as xe2x80x9cguanylurea nitratexe2x80x9d) and an oxidizing agent. This patent discloses that oxidizing agents useful in the propellant formulation thereof include nitrates of alkali and alkaline earth elements, perchlorates of alkali and alkaline earth elements, ammonium nitrate, ammonium perchlorate or mixtures of these compounds.
Those skilled in the art will appreciate that nitroaminoguanidine exists in a form which has acid characteristics and can form metallic derivatives of a highly explosive nature. Thus, compounds or materials which contain a transition metal are incompatible with nitroaminoguanidine in known automotive inflatable restraint system gas generation applications.
In addition to the above-identified desirable properties and characteristics, gas generant materials for use in automotive inflatable restraint applications must be sufficiently reactive such that upon the proper initiation of the reaction thereof, the resulting gas producing or generating reaction occurs sufficiently rapidly such that a corresponding inflatable airbag cushion is properly inflated such as to provide impact protection to an associated vehicle occupant. In general, the burn rate for a gas generant composition can be represented by the equation (1), below:
Rb=Bpnxe2x80x83xe2x80x83(1)
where,       Rb    =          burn      ⁢              xe2x80x83            ⁢      rate      ⁢              xe2x80x83            ⁢              (        linear        )                  B    =    constant        P    =    pressure                                            n            =                          xe2x80x83                        ⁢                          pressure              ⁢                              xe2x80x83                            ⁢              exponent                                ,                      xe2x80x83                    ⁢                      where            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            pressure            ⁢                          xe2x80x83                        ⁢            exponent            ⁢                          xe2x80x83                        ⁢            is            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            slope                                                                    xe2x80x83                    ⁢                      of            ⁢                          xe2x80x83                        ⁢            the            ⁢                                          xe2x80x83                            ⁢                              xe2x80x83                                      ⁢            plot            ⁢                                          xe2x80x83                            ⁢                              xe2x80x83                                      ⁢            of            ⁢                          xe2x80x83                        ⁢            the            ⁢                                          xe2x80x83                            ⁢                              xe2x80x83                                      ⁢            log            ⁢                          xe2x80x83                        ⁢            of            ⁢                                          xe2x80x83                            ⁢                              xe2x80x83                                      ⁢            pressure            ⁢                          xe2x80x83                        ⁢            along            ⁢                          xe2x80x83                        ⁢            the            ⁢                                          xe2x80x83                            ⁢                              xe2x80x83                                      ⁢            x            ⁢                          -                        ⁢            axis            ⁢                          xe2x80x83                        ⁢            versus                                                                    xe2x80x83                    ⁢                      the            ⁢                          xe2x80x83                        ⁢            log            ⁢                          xe2x80x83                        ⁢            of            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            burn            ⁢                          xe2x80x83                        ⁢            rate            ⁢                          xe2x80x83                        ⁢            along            ⁢                          xe2x80x83                        ⁢            the            ⁢                          xe2x80x83                        ⁢            y            ⁢                          -                        ⁢            axis                              
Guanidine nitrate (CH6N4O3) is a non-azide fuel with many of the above-identified desirable fuel properties or characteristics. For example, guanidine nitrate is commercially available, relatively low cost, non-toxic, provides excellent gas output due to a high content of nitrogen, hydrogen and oxygen and a low carbon content and has sufficient thermal stability to permit spray dry processing. As a result, guanidine nitrate has found wide use in the automotive airbag industry.
Unfortunately, guanidine nitrate suffers from a lower than may be desired bum rate. Further, guanidine nitrate may, when combined with certain other common gas generant formulation components, undesirably form eutectic mixtures. The lower melting points associated with such eutectic mixtures may in turn exacerbate concerns regarding the aging characteristics or properties of the gas generant formulation.
Thus, there remains a need and a demand for an azide-free gas generant material which may more effectively overcome one or more of the problems or shortcomings described above. In particular, there is a need and a demand for gas generant materials which, while effective in overcoming one or more of the problems or shortcomings identified above, also provides or results in a desirably rapid burn rate as required or desired for particular applications, while also avoiding formation of undesired eutectic mixtures.
A general object of the invention is to provide improved gas generation and, more particularly, to provide improved gas generant compositions and associated gas generant composition-containing devices and methods of gas generation.
A more specific objective of the invention is to overcome one or more of the problems described above.
In accordance with one preferred embodiment of the invention, the general object of the invention can be attained, at least in part, through a gas generating composition which includes a complex of guanylurea nitrate with at least one metal element having an atomic number of 21-30 and 39-50. The gas generating composition also includes sufficient oxidizer such that upon combustion reaction initiation of the gas generating composition reaction products including a quantity of nitrogen gas are produced.
The prior art generally fails to provide gas generant materials which, while avoiding inclusion or reliance on azide or azide-based materials, also suitably satisfies selected criteria such as relating to manufacture and performance. In particular, gas generant materials of the prior art and such as used in gas generating devices used in automotive inflatable restraint systems, for example, generally fail to provide or result in desirably high burn rates while avoiding undesired eutectic formation and while also satisfying, as effectively as desired, various manufacturing and performance criteria. For example and as described in greater detail herein, such manufacturing and performance criteria may include:
a) avoidance of inclusion or reliance on azide or azide-based materials;
b) cost;
c) safety;
d) gas output;
e) thermal stability;
f) effluent toxicity; and
g) ease of manufacture or production via water-based processing.
The invention further comprehends a method of making a gas generating composition. In accordance with a preferred embodiment of this aspect of the invention such method involves contacting a quantity of guanylurea nitrate with a quantity of a complexing agent containing at least one metal element having an atomic number of 21-30 and 39-50 sufficient to form a complex of guanylurea nitrate containing the at least one metal element.
As described in greater detail below and in accordance with a preferred practice of such aspect of the invention, such contacting may desirably occur in a water slurry such as at an elevated temperature. Further, additional gas generant composition materials or components such as oxidizers, co-fuels, additives or combinations thereof can desirably be included in such gas generating composition via addition of the same to such slurry mixture.
The invention still further comprehends, in accordance with yet another embodiment of the invention, a method of generating gas wherein a gas generant composition which contains a complex of guanylurea nitrate with at least one metal element having an atomic number of 21-30 and 39-50 and sufficient oxidizer are reacted such that upon combustion reaction initiation of the gas generating composition reaction products including a quantity of nitrogen gas are produced.
As used herein, references to a specific composition, component or material as a xe2x80x9cfuelxe2x80x9d are to be understood to refer to a chemical which generally lacks sufficient oxygen to burn completely to CO2, H2O and N2.
Correspondingly, references herein to a specific composition, component or material as an xe2x80x9coxidizerxe2x80x9d are to be understood to refer to a chemical generally having more than sufficient oxygen to burn completely to CO2, H2O and N2.
Guanylurea nitrate (NH2C(NH)NHC(O)NH2.HNO3) is also commonly known as dicyandiamidine and amidinourea.